| Abstrakt: |
Various iron salts solutions have been used to contrast blocks of renal tissue prior to their dehydration and embedment. Pure ferric ammonio-sulphate solutions give a strong contrast of the nuclear chromatin, of the mitochondria and of the basement membranes, but the electron microscopical appearance of the tissue is bad, because of the acidity of the solution. At higher pH, obtained in mixtures of ferric ammonio-sulphate and potassium sodium tartrate, the preservation is improved, the contrast of the chromatin, of the mitochondria and of the membranes decreases from a pH of 4.5. On the contrary, the cytoplasmic 'matrix' becomes more electron-opaque and takes a granular appearance. The advantages of the block-staining are discussed. Specimens contrasted by this method can be observed in the light microscope, after addition of haematoxylin to the dehydrating ethanol series. In that case, there is a complete similarity between the light-stained and the electron-contrasted areas. Moreover, the understanding of the contrast is easier after block-staining: in the case of iron, the metal is complexed by the phosphate and the sulphate radicals of the tissue, with a contrasting solution at a pH value up to 4.5. For higher pH values, the iron-tartrate complex ions play an important role, possibly even in the cationic sites of the tissue. They can thus be considered as anionic metallic contrasting agents. [ABSTRACT FROM AUTHOR] |
